What to Do if Your Car Heater isn’t Working

While it’s normal for air-con to stop working at the most inconvenient times (midsummer noon in a traffic jam) – if your car’s heater stops working, then you should pay attention: it could indicate a more serious problem. So don’t put off car checks if your car heater’s blowing out cold air.

Let’s first quickly look at how a heater works.

How does a car heater work?

We’ll not go into the complete technical detail, but it’s worth knowing that your air con and heating system are related. Essentially, they’re both using the heat and power generated by your engine to cool or warm air circulated around your vehicle.

Air con works slightly differently in that you need a refrigerant to get the air lower than the ambient air temperature, but car heaters are (in most vehicles) essentially just the engine.

The engine needs to get up to a certain operating temperature to run most efficiently, but after a certain point, it’s liable to overheat. Original car designs featured grills to cool the engine with air directed to it while the car drives – but what about when you’re stuck in traffic? Or what about when it’s an extremely hot summer’s day?

This is why liquid cooling was invented to help regulate engines at all times. Coolant liquid works by being pumped through tubes around the engine. It is then warmed by the engine's heat (therefore removing some of the heat away from the engine). As the coolant liquid continues to circulate, it forms what is known as a closed-loop system by constantly drawing heat away from the engine.

Car heaters are an extra addition to this loop. The idea is that an extra radiator is added to the loop – that radiator is placed in front of a fan that pulls air into the ducts (either from the outside or from inside the car) and passes the radiator into the vehicle itself. As the cold air passes over the now-hot radiator, it’s warmed up.

This is why it often takes a few minutes for the heating in your car to get going – because it takes a few minutes for the engine and coolant to get warm!

What does it mean if your car heating stops working?

Depending on which part has stopped working, it can mean a few things.

1.) The fan may have broken or the ducts may have become blocked

If you’ve turned the heating on but there’s no air coming through open ducts, then there’s a good chance that the problem lies with the radiator fan. Check the air grills around the outside of your car, specifically around the air intake vent.

2.) There could be a coolant leak

If the fans are running as normal at all powers, then you need to check your coolant reservoir to make sure the coolant level hasn’t dropped. If the air isn’t getting hot, then it’s possible that the coolant may have leaked to a point where there’s not enough to even cool the engine.

In this situation, your first step should be to turn off the engine and try topping up the reservoir (slowly) with more coolant.

Hopefully, it’ll only be a slow leak so that you’ve got time to get to a service centre! If the coolant quickly drains, then you’ve got a bigger problem on your hands because you shouldn’t drive your car without coolant – an overheated engine is potentially a much more costly fix than a few pipes!

3.) Faulty Wiring or Blown Fuses

Overall, a damaged wire wouldn't be the worst-case scenario since it's a relatively simple fix. However, if your car heater isn't responding, the issue could be due to a short-circuited wire or a blown fuse.

Your best bet here is to call for emergency assistance to have your car towed to an auto centre.

r.) Faulty or damaged thermostat

One of the most common causes of a car heater stopping working is a faulty or damaged thermostat. As a thermostat ages, it may start to corrode and could get stuck in the closed position. This could, in turn, prevent any coolant from reaching the radiator. Without any coolant, your engine will overheat, potentially causing very serious damage.

Trust the experts at your local Kwik Fit centre

We hope you never have to call for roadside assistance, and we strive to help you never need to. From free vehicle health checks to MOTs and a range of service packages, our team of expert technicians will help keep your car on the road. And with centres in over 600 locations across the UK, you’re sure to find a Kwik Centre near you.